Chapter 20: The Cardiovascular System: The Heart

Question 1

describe the location of the heart.

Answer 1

Location – rests on diaphragm near midline of thoracic cavity within the mediastinum

heart

• mediastinum – anatomical region that extends from the sternum to the vertebral column in the thoracic cavity, from the first rib to the diaphragm, and between the lungs.
• Apex – the tip of the left ventricle, rests on the diaphragm
• Base – opposite the apex, the posterior aspect, formed by the atria (the left mostly)
• anterior surface – deep to the sternum and ribs
• inferior surface – the part of the heart between the apex and right surface and rests mostly on the diaphragm
• right surface – faces right lung, extends from inferior surface to base
• left surface – faces left lung, extends from base to apex.

Question 2

describe the structure of the pericardium and the heart wall.

Answer 2

Pericardium – a loose-fitting membrane that encloses the heart. Allows sufficient freedom of movement for vigorous and rapid contraction

Two main parts: fibrous, serous

I. fibrous pericardium – superficial

• composed of tough, inelastic, dense irregular connective tissue
• resembles a bag that rests on and attaches to the diaphragm; its open end is fused to the connective tissues of the blood vessels in/out of heart
• prevents overstretching of the heart, provides protection, anchors heart in mediastinum
• inferior fibrous pericardium is partially fused to the central tendon of the diaphragm, therefore movement of the diaphragm (deep breathing) facilitates the movement of blood by the heart.

II. serous pericardium – deeper, thinner, more delicate membrane

• forms a double layer around heart: outer parietal and inner visceral layers
• parietal layer – outer layer; fused to the fibrous pericardium.
• visceral layer or epicardium – the outermost layer of the heart wall. i. Adheres tightly to the surface of the heart

pericardial fluid – slippery secretion of the pericardial cells

• a thin film of lubricating serous fluid.
• Reduces friction between the layers of the serous pericardium as the heart moves

pericardial cavity – the space that contains the few mL’s of pericardial fluid

layers of the heart wall – 3 layers

a. epicardium – AKA visceral layer of serous pericardium

• gives a smooth, slippery texture to the outermost surface of the heart.
• Contains blood vessels, lymphatics, and vessels that supply the myocardium
• contains two tissue layers

1. thin transparent outer layer of the heart wall is mesothelium
2. beneath the mesothelium is a variable layer of delicate fibroelastic tissue and adipose tissue

• the adipose tissue becomes thickest over the ventricular surfaces. Here it houses the major coronary and cardiac vessels of the heart
• the amount of fat varies for people; corresponds to body fat in an individual, typically increases with age

b. myocardium – middle layer, composed of cardiac muscle tissue

• responsible for the pumping action of the heart
• makes approx. 95% of the heart wall
• the cardiac muscle fibers are organized in bundles that swirl diagonally around the heart and generate the strong pumping actions of the heart.
• Striated, involuntary.

c. Endocardium – innermost layer; thin layer of endothelium overlying a thin layer of connective tissue

• Provides a smooth lining for the chambers of the heart and covers the valves of the heart
• The smoother lining minimizes surface friction as blood passes through the heart
• The endocardium is continuous with the endothelial lining of the large blood vessels attached to the heart.

Question 3

discuss the external and internal anatomy of the chambers of the heart.

Answer 3

chambers of the heart – 4 total

1. atria (2) – superficial receiving chambers.
2. ventricles (2) – inferior pumping chambers

auricle – wrinkled pouchlike structure called an auricle on the anterior surface of each atrium. i. Slightly increases the capacity of the atrium so it can hold more blood

coronary sulcus (plural is sulci) – deep groove that encircles most of the heart and marks the external boundary between the atria and ventricles i. contains blood vessels and fat

Anterior interventricular sulcus - groove on surface of heart that marks boundary b/w left and right ventricle

right atrium – forms right surface of heart, receives blood from three veins: superior vena cava, inferior vena cava, coronary sinus

• approx. 2-3 mm average thickness
• inside of posterior wall is smooth, inside of anterior wall is rough due to pectinate muscles

pectinate muscle – projecting muscle bundles of the anterior atrial walls and lining of the auricles

interatrial septum – a thin partition between the right and left atria

fossa ovalis (or foramen ovale) – oval depression; the remnant of the foramen ovale (an opening in the interatrial septum of the fetal heart that normally closes soon after birth)

tricuspid valve (or right atrioventricular valve) – valve through which blood passes from right atria into right ventricle.

1. Named for 3 cusps (superior view is a 3 part valve)
2. Composed of dense connective tissue covered by endocardium

right ventricle – forms most of the anterior surface of the heart

• about 4-5 mm thick
• trabeculae carnae – (muscular ridges) raised bundles of cardiac muscle fibers that form a series of ridges inside the right ventricle
• chordae tendineae – tendonlike, fibrous cords that connect atrioventricular valves of the heart with papillary muscles
• papillary muscles – cone shaped trabeculae carneae which the chordae tendineae are connected to.
• interventricular septum – separates the right ventricle from the left ventricle
• pulmonary valve – valve through which blood leaves the right ventricle and enters the large artery called the pulmonary trunk the pulmonary trunk divides in to right and left pulmonary arteries

left atrium – forms most of the base of the heart

also 2-3mm thick

• receives blood from lungs through four pulmonary veins
• both the posterior and anterior walls of the left atrium are smooth (pectinate muscles are confined to the auricle of the left atrium)
• bicuspid valve or mitral valve (or left atrioventricular valve) – valve through which blood passes from left atrium into left ventricle. 1. Has 2 cusps, from superior view, looks like a line across with two sides to the valve.

left ventricle – forms the apex of the heart

• thickest chamber, averages 10-15mm thick
• contains trabeculae carneae and has chordae tendineae that anchor the cusps of the bicuspid valve to papillary muscles.
• aortic valve – blood passes from left ventricle into ascending aorta through the aortic valve
• some blood flows into the coronary arteries which branch from the ascending aorta and carry blood to the heart wall.
• The remaining blood passes into the aortic arch and descending aorta (thoracic aorta and abdominal aorta).
• ligamentum arteriosum – remnant of the ductus arteriosus which connects the arch of the aorta and pulmonary trunk. 1. ductus arteriosus – temporary fetal blood vessel that shunts blood from the pulmonary trunk into the aorta making most fetal blood bypass the nonfunctioning fetal lungs

Question 4

relate the thickness of the chambers of the heart to their functions.

Answer 4

myocardial thickness and function – thicker heart wall for the chambers that work harder

• the atria pump blood under less pressure to the adjacent ventricles
• both ventricles act as separate pumps but simultaneously eject equal volumes of blood.
• the right ventricle pumps blood under less pressure to the lungs with a small blood flow resistance. the lumen is somewhat crescent-shaped
• the left ventricle pumps blood great distances under higher pressure, with larger blood flow resistance.
• Therefore the left ventricle works much harder than the right to maintain the same rate of blood flow
• The lumen is circular, decreasing resistance

fibrous skeleton of the heart – dense connective tissue within the heart wall in addition to cardiac muscle tissue

• consists of 4 dense connective tissue rings that surround the valves of the heart, fuse with one another, and merge with the interventricular septum.
• Forms a structural foundation for the heart valves and prevents overstretching of the valves as blood passes through them.
• Also serves as insertion point for bundles of cardiac muscles and acts as an electrical insulator between the atria and ventricles.

Question 5

outline the flow of blood through the chambers of the heart and through the systemic and pulmonary circulations.

Answer 5

operation of heart valves – open and close in response to pressure changes as the heart contracts and relaxes made of Dense connective tissue

• help ensure one-way flow of blood

atrioventricular (AV) valves – between the atria and ventricles

• formed by membranous flaps (cusps)
• when opened, the cusps project into the ventricle
• valve opens when the ventricles are relaxed and the papillary muscles are relaxed and the chordeae tendinae are slack – blood in atria is under higher pressure so moves to lower pressure area in the ventricle
• contraction of the ventricle increases the blood pressure which drives the cusps upward into closed position. At the same time, papillary muscles contract and pull on the chordeae tendinae, preventing the cusps from opening into the atria
• if the papillary muscles or chordeae tendinae are damaged, blood may back flow into the atria.

semilunar (SL) valves – between the ventricles and blood vessels – pulmonary trunk or aorta. – AKA aortic and pulmonary valves. Named for the 3 crescent shaped cusps they are made up of.

• Each cusp attaches to the arterial wall by its convex outer margin
• The SL valves allow blood to exit heart into arteries but prevents blood flow back into the ventricles
• The free borders of the cusps project into the lumen of the artery.
• When the ventricle contracts, pressure builds within the chambers.
• SL valves open when pressure in ventricles exceeds pressure in arteries
• As the ventricle relaxes, backflowing blood fills the cusps and they close.

Venous backflow prevention – no valves between veins and atria. Backflow is minimized by the atrial contractions compressing and nearly collapsing the weak walls of the venous entry points.

circulation of blood – post-natal circulation consists of two closed circuits

• systemic circulation – oxygenated blood flows from left ventricle through the aorta and all areas of the body and deoxygenated blood returns to the right atrium Coronary artery brings oxygenated blood to mycocardium
• pulmonary circulation – deoxygenated blood flows from right ventricle to lungs and returns oxygenated blood to the left atrium

right atrium and right ventricle contain deoxygenated blood

Question 6

discuss the coronary circulation.

Answer 6

coronary circulation or cardiac circulation – the pathway followed by the blood from the ascending aorta through blood vessels supplying the heart and returning to the right atrium

coronary arteries – branch from the ascending aorta

• encircle the heart like a crown
• while heart is contracting, little blood enters because they are squeezed shut. When the heart relaxes, high aortic BP propels blood through the coronary arteries, into capillaries, and then into coronary veins.
• Two coronary arteries branch from the ascending aorta: left and right coronary arteries
• Left coronary artery – passes inferior to the left auricle, divides into the anterior interventricular and circumflex branches

1. Anterior interventricular branch (or left anterior descending LAD artery) – lies in the anterior interventricular sulcus
2. Supplies walls of both ventricles
3. Circumflex branch – lies in the coronary sulcus, supplies walls of left ventricle and left atrium

Right coronary artery – first supplies small branches to the right atrium, then continues inferior to the right auricle and divides into the posterior interventricular and marginal branches

• Atrial branches – small branches to the right atrium
• Posterior interventricular branch – follows the posterior interventricular sulcus, supplies the walls of the two ventricles
• Marginal branch – beyond the coronary sulcus, runs along the right margin of the heart, supplies the wall of the right ventricle

Anastomoses – connections between arteries that provide alternate routes for blood to reach a particular organ or tissue

• In most parts of the body, blood is received from branches of more than one artery, and where two or more arteries supply the same region, they usually connect.
• These connections are called anastomoses and provide collateral circulation

collateral circulation – alternate route taken by blood through an anastomosis

• myocardium contains many anastomoses that connect branches of a coronary artery or extend between branches of different coronary arteries
  
  • provide detours for arterial blood if a main route becomes obstructed, allowing heart muscle to receive sufficient oxygen even if one of its coronary arteries is partially blocked.
• coronary veins – receive deoxygenated blood from cardiac capillaries and return it to the right atrium. a. Most deoxygenated blood from the myocardium drains into a large vascular sinus in the coronary sulcus on the posterior surface of the heart.
• coronary sinus – a wide venous channel on the posterior surface of the heart that collects the blood from the coronary circulation and returns it to the right atrium.
• A vascular sinus is a thin walled vein that has no smooth muscle to alter its diameter.
• Principal veins that supply the coronary sinus:

1. Great cardiac vein – in the anterior interventricular sulcus 1. Receives blood from the left coronary artery (L and R ventricles and L atrium)
2. Middle cardiac vein – in the posterior interventricular sulcus 1. Receives blood from the posterior interventricular branch of the right coronary artery (L and R ventricles)
3. Small cardiac vein – in the coronary sulcus 1. Drains the right atrium and right ventricle
4. Anterior cardiac veins – drain the right ventricle and open directly into the right atrium

Reperfusion – reestablishment of blood after blockage of a coronary artery deprives the heart muscle of oxygen

• Can further damage tissue due to formation of oxygen free radicals
  
  • Molecules that have an unpaired electron
  • Highly unstable, highly reactive molecules cause chain reactions that lead to cell damage and death
  • Body cells produce enzymes to convert free radicals to less reactive substances (superoxide dismutase and catalase), and also nutrients such as vitamins E, C, beta-carotene, zinc, and selenium all serve as antioxidants and remove oxygen free radicals from circulation

Question 7

describe the structural and functional characteristics of cardiac muscle tissue and the cardiac conduction system

Answer 7

cardiac muscle tissue and the cardiac conduction system

histology of cardiac muscle

. compared to skeletal muscle fibers – cardiac are shorter and less circular in transverse section

• exhibit branching, giving individual cardiac muscle fibers a stairstepping appearance
• typically 50-100micrometers long, diameter of 14 micrometers
• usually 1 central nucleus, occasionally a 2nd nucleus
• larger more numerus mitochondria that take up 25% of cytosolic space (only 2% in skeletal muscle fibers)
• same arrangement of actin and myosin, same bands, zones, and Z discs as skeletal muscle fibers
• transverse tubules of cardiac muscle are wider, but less abundant than in skeletal muscle
• a single transverse tubule per sarcomere is located at the Z disc.
• Sarcoplasmic reticulum is somewhat small in cardiac muscle fibers and cardiac muscle has a smaller intracellular reserve of Ca2+

intercalated discs – irregular transverse thickenings of the sarcolemma that connect the ends of cardiac muscle fibers to neighboring fibers

desmosomes – within intercalated discs, hold neighboring cardiac muscle fibers together

gap junctions – within intercalated discs, allow rapid conduction of muscle action potentials

• allow the entire atria or ventricles to contract as a single, coordinated unit.

autorhythmic fibers – cells that repeatedly and rhythmically generate action potentials

• a network of specialized cardiac muscle fibers
• relatively rare – during embryonic development, about 1% of the cardiac muscle fibers become autorythmic fibers
• Two important functions: pacemaker and cardiac conduction system

Pacemaker – the autorhythmic fibers set the rhythm of electrical excitation that causes contraction of the heart

cardiac conduction system – network of specialized cardiac muscle fibers that provide a path for each cycle of cardiac excitation to progress through the heart.

• The conduction system ensures that cardiac chambers become stimulated to contract in a coordinated manner, making the heart an effective pump.
• The system includes the SA node, the AV bundle, the R and L bundle branches, and Purkinje fibers

sinoatrial (SA) node – a small mass of cardiac muscle fibers

1. located in the right atrium inferior to the opening of the superior vena cava
2. spontaneously depolarize and generate a cardiac action potential about 100x per minute.
3. AKA natural pacemaker

pacemaker potential – the spontaneous depolarization of SA node cells

• when the pacemaker potential reaches threshold, it triggers an
• action potential.
• Each action potential from the SA node propagates throughout both atria via gap junctions in the intercalated discs of atrial muscle fibers.
• Following the action potential, the two atria contact in unison.
  
  • the action potential slows considerable at the AV node

atrioventricular (AV) node – compact mass of conducting cells located in the interatrial septum

• this delay provides time for the atria to empty their blood into the ventricles

atrioventricular (AV) bundle or bundle of His – begins at the AV node and passes through the cardiac skeleton separating the atria and the ventricles, then extends a short distance down the interventricular septum before splitting into right and left bundle branches.

• the only site in the heart where action potentials can conduct from the atria to the ventricles.

left and right bundle branches – extend through the interventricular septum toward the apex of the heart

Purkinje fibers – large-diameter cardiac muscle fibers in the ventricular tissue of the heart specialized for conducting an action potential to the myocardium

• Rapidly conduct the action potential beginning at the apex of the heart upward to the remainder of the ventricular myocardium.
• Then the ventricles contract, pushing blood upward toward the semilunar valves.

artificial pacemaker – a device that sends out small electrical currents to stimulate the heart to contract

• surgically implanted
• consists of a battery and impulse generator
• usually implanted beneath the skin inferior to the clavicle.
• Connected to one or two flexible wire leads that are threaded through the superior vena cava into the various chambers of the heart.
• If the SA node is damaged or diseased, the AV node can do pacemaking, about 40-60 beats per minute. If both the SA and AV nodes are damaged, the AV bundle, a bundle branch, or Purkinje fibers can provide autorhythmicity, but too slow, 20-35 beats per minute, so brain is not sufficiently provided with oxygen and an artificial pacemaker is required.

Question 8

explain how an action potential occurs in cardiac contractile fibers.

Answer 8

action potential initiated by SA node, travels along the conduction system and spreads out to excite the “working” atrial and ventricular muscle fibers

Cardiac Action Potential structures SA node, AV node, Bundle of His, Purkinje fibers

contractile fibers – the “working” cardiac muscle fibers – atrial and ventricular muscle fiber cells that contract when excited by the action potential propagated by the SA node.

action potential stages – 3 stages, depolarization, plateau, and repolarization

1. Depolarization – contractile fibers have a stable resting membrane potential around -90mV.

• When brought to threshold by an action potential from neighboring fibers, voltage-gated fast Na+ channels open.

voltage gated fast Na+ channels – sodium ion channels referred to as “fast” because they open very rapidly in response to a threshold-level depolarization

• opening allows Na+ inflow because the cytosol of contractile fibers is electrically more negative than interstitial fluid which has a higher Na+ concentration than the cytosol.
• rapid depolarization – produced by inflow of Na+ down the electrochemical gradient
• within a few milliseconds, the fast Na+ channels automatically inactivate and Na+ inflow decreases.

2. Plateau – middle phase of action potential in a cardiac contractile fiber

1. A period of maintained depolarization
2. Due in part to opening of voltage gated slow Ca++ channels
3. Lasts about 0.25 second and the membrane potential of the contractile fiber is close to 0 mV

• (remember, depolarization of a neuron of skeletal fiber is way briefer about 0.001 second, because they lack plateau phase)

voltage gated slow Ca++ channels – when opened, Ca2+ move from interstitial fluid into the cytosol.

• This inflow causes even more Ca2+ to pour out of the SR into the cytosol through additional Ca2+ channels in the SR membrane
• The increased Ca2+ concentration in the cytosol ultimately triggers contraction

I. voltage gated K+ channels – also found in the sarcolemma of a contractile fiber

• several different types
• just before plateau phase begins, some K+ channels open, allowing potassium ions to leave the cytosol
• therefore depolarization is sustained during plateau phase because Ca2+ inflow just balances K+ outflow

3. repolarization – recovery of the resting membrane potential

• resembles that in other excitable cells
• after a delay (prolonged in cardiac muscle), additional voltage-gated K+ channels open

1. outflow of K+ restores the negative resting membrane potential (-90 mV)
2. at the same time, the calcium channels in the sarcolemma and the SR are closing, also contributing to repolarization.

refractory period – time interval in which a second contraction cannot be triggered the refractory period of a cardiac muscle fiber lasts longer than the contraction itself

• therefore another contraction cannot begin until relaxation is well underway.
• Therefore tetanus cannot occur in cardiac muscle (but can in skeletal muscle)

Question 9

describe the electrical events of a normal electrocardiogram.

Answer 9

electrocardiogram or ECG or EKG – a recording of the electrical changes that accompany the cardiac cycle that can be detected at the surface of the body; may be resting, stress, or ambulatory

electrocardiograph – the instrument used to record the changes in an ECG.

• 12 leads, 6 on limbs, 6 on chest which produce 12 tracings from different combo’s of limb and chest leads
• Possible to determine if the conduction pathway is abnormal, if the heart is enlarged, if certain regions of the heart are damaged, and the cause of chest pain

3 clearly recognizable waves occur with each heartbeat in a typical record

1. P wave – first wave, a small upward deflection on the ECG

a. Signifies atrial depolarization

atrial depolarization – spreads from the SA node through contractile fibers in both atria

2. QRS complex – second wave, begins as a downward deflection, continues as a large upright triangular wave, and ends as a downward wave

• Represents rapid ventricular depolarization

ventricular depolarization – the action potential spreads through ventricular contractile fibers

plateau – during plateau period of steady depolarization, the ECG tracing is flat

• the space between end of QRS and T waves (the S-T segment)

3. T wave – third wave, dome shaped upward deflection

• Indicated ventricular repolarization
• Smaller and wider than the QRS complex because repolarization occurs more slowly than depolarization.

ventricular repolarization – occurs just as the ventricles are starting to relax

correlation of ECG waves with atrial and ventricular systole

1. systole – in the cardiac cycle, the phase of contraction of the heart muscle, especially of the ventricles
2. diastole – in the cardiac cycle, the phase of relaxation of dilation of the heart muscle, especially of the ventricles
3. The ECG waves predict the timing of atrial and ventricular systole and diastole.

Question 10

describe the pressure and volume changes that occur during a cardiac cycle.

Answer 10

cardiac cycle – a complete heartbeat

• consists of systole and diastole of both atrial and ventricles
• pressure and volume changes – in each cardiac cycle, the atria and ventricles alternately contract and relax, forcing blood from higher pressure areas to lower pressure areas.

1. As a chamber of the heart contracts, the blood pressure within it increases.
2. Pressure within left chambers is higher than pressure in right chambers but each ventricle expels that same volume of blood.

atrial systole – the atria are contracting

• lasts about 0.1 second
• the ventricles are relaxed
• depolarization of the SA node causes atrial depolarization, marked by the P wave in the ECG
• atrial depolarization causes atrial systole. As the atria contract, they exert pressure on the blood within, which forces blood through the open AV valves into the ventricles
• atrial systole contributes a final 25mL of blood to the volume already in each ventricle (about 105mL). The end of atrial systole is also the end of ventricular diastole (relaxation). Thus, each ventricle contains about 130mL at the end of its relaxation period (diastole).

end diastolic volume (EDV) – the blood volume each ventricle contains at the end of its relaxation period (diastole).

• The QRS complex in the ECG marks the onset of ventricular depolarization

ventricular systole – the ventricles are contracting

• lasts about 0.3 second
• at the same time, the atria are relaxed in atrial diastole
• ventricular depolarization causes ventricular systole.
• As ventricular systole begins, pressure rises in the ventricles and pushes blood up against the AV valves, forcing them shut.
• For about 0.05 second, both the SL and AV valves are closed.

isovolumetric contraction – the period during which both SL and AV valves are closed. Cardiac muscle fibers are contracting and exerting force but are not yet shortening. Thus, the muscle contraction is isometric (same length) and because all 4 valves are closed, the ventricular volume remains the same (isovolumic)

• continued contraction of the ventricles causes pressure inside the chambers to rise sharply.

ventricular ejection – the period when the SL valves are open

• lasts about 0.25 second
• when left ventricular pressure surpasses aortic pressure at about 80mmHg and right ventricular pressure rises about the pressure in the pulmonary trunk (about 20mmHg), both SL valves open.
• The pressure in the left ventricle continues to rise to about 120mmHg and pressure in the right ventricle climbs to about 25-30mmHg.
• The ventricles eject about 70mL of blood into the aorta/pulmonary trunk.

end systolic volume (ESV) – the volume of blood remaining in each ventricle at the end of systole

• about 60mL

stroke volume – the volume ejected per beat from each ventricle

• equals end-diastolic volume minus end-systolic volume

1. SV = EDV – ESV
2. At rest, the stroke volume is about 70mL

• The T wave in the ECG marks the onset of the ventricular repolarization

relaxation period – the atria and ventricles are both relaxed.

• Lasts about 0.4 second
• With increased heart rate, relaxation period becomes shorter whereas the duration of atrial systole and ventricular systole shorten only slightly
• Ventricular repolarization causes ventricular diastole
  
  • Backflowing blood catches in the valve cusps and closes the SL valves

ventricular diastole – as ventricles relax, pressure within the chambers falls, blood in the aorta and pulmonary trunk begin to flow backward toward the lower pressure regions in the ventricles.

• The aortic valve closes at a pressure of about 100mmHg

dicrotic wave – rebound of blood off the closed cusps of the aortic valve produces the dicrotic wave on the aortic pressure curve.

isovolumetric relaxation – the brief interval when ventricular blood volume does not change because all 4 valves are closed.

• As the ventricles continue to relax, the pressure falls quickly.

ventricular filling – begins when ventricular pressure drops below atrial pressure and the AV valves open

• blood that has been flowing into and building up in the atria during ventricular systole then rushes rapidly into the ventricles
• the majority of ventricular filling occurs just after the AV valves open.
• Blood that has been flowing into the and building up into the atria during ventricular systole then rushes rapidly into the ventricles.
• At the endo f the relaxation period, the ventricles are about ¾ full.
• The P wave appears in the ECG, signaling the start of another cardiac cycle.

Question 11

relate the timing of heart sounds to the ECG waves and pressure changes during systole and diastole.

Answer 11

heart sounds – 4 heart sounds but only the first 2 are loud enough to hear with a stethoscope in a normal heart.

Lubb sound – louder, a bit longer than the second sound

• Caused by blood turbulence associated with closure of the AV valves soon after ventricular systole begins

dupp sounds – second sound, shorter and quieter than the first.

• Caused by blood turbulence associated with the closure of the SL valves at the beginning of the ventricular diastole.

Both Lubb and dupp are best heard at the surface of the chest slightly away from the location of the valve itself as the sound is carried away from the valves by the blood.

heart murmurs – an abnormal sound that consists of a flow noise that is heard before, between, or after the normal heart sounds, or that may mask normal heart sounds.

• Extremely common in children, not usually a health condition
• Frequently discovered in kids between 2-4 years, called innocent or functional heart murmurs and usually subside or disappear with growth.
• Most often, murmurs in adults indicate a valve disorder.

Stenosis – valve produces a murmur when the valve should be fully open but is not

• Mitral stenosis – murmur during relaxation period, between S2 and the next S1.

Incompetent heart valve – murmur appears when the valve should be fully closed but is not

• Mitral incompetence murmur – occurs during ventricular systole, between S1 and S2.

Question 12

define cardiac output.

Answer 12

cardiac output (CO) – the volume of blood ejected from the ventricle into the aorta (left) or pulmonary trunk (right) each minute

• cardiac output (CO) = stroke volume (SV) × heart rate (HR)

1. in a typical resting male, stroke volume averages 70mL/beat and heart rate is about 75 beats/ minute so 70mL/beat x 75beats/min = 5250mL/min
2. 5.25 L/min
3. This volume is close to the total blood volume, thus, your entire blood volume flows through your pulmonary and systemic circulations each minute.
4. Factors that increase stroke volume or heart rate normally increase CO.
5. Example: exercise increases stroke volume and heart rate

cardiac reserve – difference between a person’s maximum cardiac output and cardiac output at rest.

1. The average person has a cardiac reserve of 4-5x resting value
2. Top endurance athletes may have a cardiac reserve 7-8x their resting CO.
3. People with severe heart disease may have little or no cardiac reserve, which limits their ability to carry out even simplest tasks of life.

regulation of stroke volume – 3 factors affect stroke volume and ensure that the left and right ventricles pump equal volumes of blood: preload, contractility, afterload.

preload (effect of stretching) – the degree of stretch on the heart before it contracts

• Frank Starling law of the heart – relationship between the amount that the heart fills with blood during diastole and the strength of contraction during systole
• The more the heart fills, the greater the force of contraction
• Normally, the greater the end-diastolic volume (EDV) the more forceful the next contraction
• Two key factors determine EDV: duration of ventricular diastole and venous return
• The Frank-Starling law of the heart equalizes the output of the right and left ventricles and keeps the same volume of blood flowing to both systemic and pulmonary circulations.

1. If the left side pumps a little more blood than the right side, the volume of blood returning to the right ventricle (venous return) increase. The increased EDV causes the right ventricle to contract more forcefully on the next beat, bringing the two sides back into balance.
2. When heart rate increases, the duration of diastole is shorter. Less filling time means a smaller EDV and the ventricles may contract before they are fully filled.

venous return – the volume of blood returning to the right ventricle

• when venous return increases, a greater volume of blood flowsmin to the ventricles, and the EDV is increased.
• Heart rate above 160 BPM means stroke volume usually declines due to short filling time.
• At such rapid heart rates, EDV is less, and preload is lower.
• People with slow resting heart rates usually have larger resting stroke volumes because filling time is prolonged and preload is larger.

contractility – the forcefulness of contraction of individual ventricular muscle fibers

• the strength of contraction at any given period.
• positive and negative inotropic agents – substances that increase (positive) and decrease (negative) contractility
• for a constant preload, the stroke volume increases when a positive inotropic substance is present

1. positive inotropic agents often promote Ca2+ inflow during cardiac action potentials which strengthens the force of the next contraction.
2. Positive inotropic agents:
3. Stimulation of the sympathetic division of the autonomic nervous system
4. Hormones such as epinephrine and norepinephrine
5. Increased Ca2+ level in the interstitial fluid
6. Drug: digitalis
7. Negative inotropic agents:
8. Inhibition of the sympathetic division of the ANS
9. Anoxia
10. Acidosis
11. Some anesthetics
12. Increased K+ level in the interstitial fluid
13. Drugs: Calcium channel blockers – can have negative inotropic effect by reducing Ca2+ inflow, thereby decreasing the strength of the heart beat.
    
    1. Ejection of blood from the heart begins when pressure in the right ventricle exceeds the pressure in the pulmonary trunk and when the pressure in the left ventricle exceeds pressure in the aorta.

afterload – the pressure that must be exceeded before ejection of blood from the ventricles can occur.

• At that point, the higher pressure in the ventricles causes blood to push the semilunar valves open.
• The pressure that must be overcome before a semilunar valve can open is termed the afterload.
• An increase in afterload causes stroke volume to decrease, so that more blood remains in the ventricles at the end of systole.
• Conditions that can increase afterload include hypertension (htn), and narrowing of arteries by atherosclerosis.

regulation of heart rate – affected by homeostatic mechanisms

• factors that contribute to regulation of heart rate: ANS and hormones released by the adrenal medullae (epinephrine and norepinephrine)

autonomic regulation of heart rate

• cardiovascular center – groups of neurons scattered within the medulla oblongata that regulate heart rate, force of contraction, and blood vessel diameter.

1. Medulla receives input from a variety of sensory receptors and from higher brain centers such as the limbic system and the cerebral cortex.
2. The cardiovascular center then directs appropriate output by increasing or decreasing the frequency of nerve impulses in both the sympathetic and parasympathetic branches of the ANS.

• Proprioceptors – monitoring the position of limbs and muscles; send nerve impulses at an increased frequency to the cardiovascular center
  1. A major stimulus for the quick rise in heart rate that occurs at the onset of physical activity.
• Chemoreceptors – monitor chemical changes in the blood
• Baroreceptors – monitor the stretching of major arteries and veins

Question 13

describe the factors that affect regulation of stroke volume.

Question 14

outline the factors that affect the regulation of heart rate.